Generalize `GetNoteError` endopint

[bobbinth]

In #1792, we introduced GetNoteError endpoint, but I think we could generalize it to something like GetNetworkNoteStatus endpoint.

The endpoint would take a note ID as an input, and would return:

• "Not found" if the note doesn't exist or is not a network note.
• Status of the note - maybe:
  • pending - we are still trying to execute this note (whether there were errors or not).
  • processed - the note made it into a transaction which was sent to the block producer.
  • committed - the network is now in the store.
  • discarded - the note failed too many times and won't be retried in the future.
• The last error associated with the note execution - basically, what GetNoteError returns now (this is applicable for all status above).

This will provide an easy way for users to figure out if an error was a transient error that was resolved, or if the note is now fully discarded.